In the papermaking industry, “sizing” is the treatment of paper which gives it resistance to the penetration of liquids (particularly water) or vapors. Sizing is also employed to improve ink holdout. Imparting such resistance to hydrophilic liquid penetration (normally water) is an important property of paper, both in the papermaking process and in the final product. Sizing agents are used in the papermaking process to increase wood fiber's resistance to liquid penetration. The resistance to the absorption of liquids is desired when the paper product is purposefully wetted during a converting process (printing or laminating) or accidentally wetted (packaging containers or newspapers).
Generally, resistance to water penetration is achieved by the introduction of a sizing agent at the wet-end of the papermaking process. A common sizing agent is alkenyl succinic anhydride (“ASA”). Alkenyl succinic anhydride (ASA) is an internal sizing agent, which is commonly used to treat fibers in the papermaking process, making them more hydrophobic. Internal sizing refers to the treatment of the wood fibers prior to forming a wet web. ASA is a water insoluble oil that is essentially nonionic in nature. Therefore, ASA must be emulsified before it is added to the papermaking process. Emulsification of ASA produces an oil-in-water emulsion and also cationizes ASA emulsion droplets. Cationizing the ASA droplets helps to promote emulsion stability and aids in ASA retention. Common cationic emulsifiers for ASA include derivatized starches and synthetic acrylamide-based polymers.
Application of sizing agents involves numerous considerations. For example, the extent to which a paper is weakened by the rewetting at the size press during production is influenced by its degree of sizing. Additionally, a high level of internal sizing of a sheet contributes to the sheet's structural stability in environments where the sheet may come in contact with liquid water. Beverage and food packaging are typical examples of the use of board and paper products where a high level of sizing is desirable.
A drawback to using ASA as a sizing material is that ASA is not water soluble and typically must be uniformly suspended in the pulp as an emulsion so that the ASA can make adequate contact with the cellulosic fibers and, thus, create the desired effect on the final product. Efforts to address performance of ASA have been made. However, conventional methods can have issues regarding shelf life, emulsion stability and equipment use.
Despite available technologies, there exists a need to improve or enhance sizing performance and efficiency in paper production processes. There also exists an ongoing industrial need in the papermaking industry to develop sizing formulations and methods that improve sizing of paper and paperboard and provide enhancements to the papermaking process.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR § 1.56(a) exists.